In general, in order to fabricate a semiconductor device, a semiconductor wafer has to be subjected to various processes such as a film-forming process, an oxidation process, a diffusion process, an etching process, and an annealing process. Even in the film-forming process, various film-forming processes are performed to form, for example, an insulating film and films containing different metals.
In these years, a so-called cluster tool has widely been used as a vacuum process system wherein process chambers for performing the above-mentioned various processes are properly combined and the process chambers are connected by a transfer chamber, with a view to enhancing a through-put, improving a countermeasure against particles, preventing formation of a natural oxide film, etc.
FIG. 18 is a schematic view showing the structure of such a conventional vacuum process system 2. As is shown in the Figure, in the vacuum process system 2, three process chambers 6A, 6B and 6C, for example, are coupled to a transfer chamber 4 via gate valves G1 to G3. In addition, two cassette chambers 8A and 8B are connected to the transfer chamber 4 via gate valves G4 and G5. A flexible and rotatable transfer arm 10 provided in the transfer chamber 4 is driven to take in a semiconductor wafer W from a cassette C, and transfer the wafer W into a desired chamber or among the process chambers 6A, 6B and 6C. In this case, the kinds of processes to be carried out in the process chambers 6A to 6C are properly chosen according to necessity, and the process chambers corresponding to these processes are provided.
In the above-described vacuum process system, the single transfer arm 10 manages, conveys and transfers wafers W among the three process chambers 6A to 6C and two cassette chambers 8A and 8B. Thus, the transfer arm 10 is required to move in a very complex manner, and the through-put deteriorates. In particular, the process time in each of the process chambers 6A to 6C is shortened by the enhancement of the performance of each process chamber, and accordingly the movement of the transfer arm 10 becomes more complex and the through-put further deteriorates.
Besides, there is a tendency that semiconductor devices have multi-layer structures, and it is necessary to form multi-layer films containing different kinds of metals. Because of this, in some cases, process chambers using film-forming gases containing different metals may be combined. Under the circumstances, the following problem arises in the vacuum process system with the above-described structure. That is, even if the inside of the process chamber is evacuated following N2 purge, etc. after the process is completed, a slight amount of metal gas, etc. enters the transfer chamber 4 at the time of transfer of the wafer W, thus disadvantageously contaminating the semiconductor wafer W with the metal. More specifically, in the vacuum process system having the above-described structure, the process chambers 6A to 6C are radially arranged around the polygonal transfer chamber 4 and the openings of the process chambers 6A to 6C are directed to the central part of the transfer chamber 4. Thus, when the process chambers 6A to 6C are opened, cross-contamination may occur between adjacent process chambers.
Furthermore, since plural process chambers 6A to 6C are provided relative to the single transfer chamber 4, the operations of all the process chambers must be stopped when any one of the process chambers has malfunctioned or requires maintenance.
Besides, the process chambers need to be spaced apart (with intervals) in consideration of the maintenance of the process chambers 6A to 6C or the transfer arm 10 in the transfer chamber 4. Consequently, the size of the whole apparatus as well as the cost will increase.